you need the big burd of prey which is currently being used in Dumfries town centre in an attempt to scare em off.
There has been a problem for years in town, now it is affecting surrounding areas due to above.
Dumfries has a river and the nearby Solway Firth so seagulls are to be expected. We have also recently covered our local refuse centre, it is all indoors, machine handled now by some new pioneering technology/system(big grey shed).
Biggest problem is people leaving out food(bin bags) which tends to be what they are coming inland to forage for. Remove food source and hey presto no(less)gulls.
You cannot shoot/kill gulls, they are protected by the very stupid law.
Find and destroy eggs(not nest), seems to work as birds return to same place every year. Apparently they live/fly within a 35ml radius
http://bird-habitats.suite101.com/article.cfm/seagull_summit_held_in_dumfries